Electrolytic process for producing amines



March 6, 1956 e. w. BODAMER 2,737,486

ELECTROLYTIC PROCESS FOR PRODUCING AMINES Filed April 1. 1952 4 IN V EN TOR.

GEORGE W. BODAMER ATTORNEY United States Patent ELECTROLYTIC PROCESS FOR PRODUCING AMINES George W. Bodamer, Cheltenham, Pa., assignor to Rohm & Haas Company, Philadelphia, Pa., a corporation of Delaware Application April 1, 1952, Serial No. 279,903

3 Claims. (Cl. 204-72) This invention relates to the production of free amines. It relates to the conversion of water-soluble acid salts of amines to free amines without the utilization of chemicals. It relates to a process of producing free amines by the electrolysis of water-soluble amine acid salts in an electrolysis cell which contains an anionic permselective membrane between the anode and the cathode. More specifically it relates to the electrolytic process for converting water-soluble acid salts of amines into free amines which process comprises passing an electric current through an electrolysis cell which has a cathode compartment, containing an aqueous solution of an acid salt of an amine, and an anode compartment containing an aqueous solution of electrolyte, preferably a strong mineral acid, said cathode and anode compartments being separated by an anionic permselective film which contains at least 25 by weight of an anion-exchange resin.

In the commercial preparation of amines the amines are first obtained in the form of their acid salts; e. g., their salts of hydrochloric or sulfuric acids. The normal pro cedure for freeing the amines is to treat the amine salts with a basic materialusually sodium hydroxide-and thereby neutralize the acid which is in combination with the amine and liberate the free amine.

One object of this invention is to provide an improved process for liberating free amines from amine salts. Another object is to eliminate the use of inorganic bases and the formation of the corresponding inorganic salts. Still another object is to use electric power instead of chemicals as a means of making free amines.

These and other objects are achieved according to the process of this invention by electrolyzing an aqueous so lution of an amine salt in a special kind of an electrolysis cell which can best be understood by a reference to the attached drawing wherein the single figure is a diagrammatical representation of a simple but typical electrolysis cell which is divided into an anode compartment and a cathode compartment by means of an anionic permselective film or membrane. In said figure 1 represents a container which is divided into two compartments, 5 and 6, by an anionic permselective membrane, 2, which is described below in greater detail. Compartment 5 is an anode compartment by virtue of the presence there of anode 3, while compartment 6 is a cathode compartment because it contains cathode 4. When the cell is in oper- In the operation of the process, an aqueous solution of an amine salt; e. g., the sulfuric acid salt of ethylenediamine, is placed in the cathode compartment 6 and a dilute solution of an acid-in this case, sulfuric acid-is placed in the anode compartment 5. A current of electricity is passed through the cell and the ions in the two compartments migrate toward the electrode of opposite charge. The sulfate ions resulting from the ionization of the sulfuric acid salt migrate toward the anode 3, pass through the anionic permselective membrane 2, into the anode compartment 5. At the anode they form sulfuric acid, which remains in solution, and at the same time oxygen is liberated in accordance with the established laws of electrolysis. (In the case of an amine hydrochloride, the chloride ions migrate through the anionic permselective membrane, are discharged at the anode and molecular chlorine is liberated-again in accordance with the laws of electrolysis.) The hydrogen ions of the acid in the cathode compartment migrate to the cathode, are discharged and liberated as molecular hydrogen. The hydrogen ions in the anode compartment tend also to migrate to the cathode but they are constrained by the anionic permselective membrane 2 which, by virtue of its being anionically permselective, repels the positive ions and confines them to the anode compartment. Thus the concentration of sulfuric acid is gradually built up in the anode compartment. (In the case of the hydrochloride salts chlorine is continuously liberated.)

It will be noted that no base is required in the instant process. Furthermore, hydrogen and oxygen or chlorine are obtained. Also in the case of the amine salts of sulfuric acid, the acid is recovered in the anode compartment and can be used in the process which produces the amine salts.

The cell which is employed in this invention can be varied as to size, shape, closures, construction materials, controls, embellishments, et cetera. What is essential, however, is that the celland by cell is meant the complete apparatus for carrying out the invention-have two compartments, one containing the anode and the other containing the cathode, and that the two compartments be separated by an anionic permselective membrane as defined herein.

The anionic permselective membrane which divides the electrolysis cell into the two compartments is all important to the success of the process. It is a diaphragm which functions by allowing only one kind of ions, namely, anions, to pass through it while at the same time preventingor at least restrainingthe passage of cations through it from one compartment to the other. i

The composition of the anionic permselective film or membrane can vary within reasonable limits but it is essential to this invention that the membrane contain at least 25% by weight of an anion-exchange resin. The permselective films which have proven to be most suitable for use in this process are those made by. incorporating particles of an anion-exchange resin in a film-forming matrix such as polyethylene, polyvinyl'chloride, natural rubber or synthetic rubber. Such films are the subject of my application, Serial No. 205,413, filed January 10, 1951, now Patent No. 2,681,319, issued June 15, 1954, to which reference is made, and they contain from 25% to of an anion-exchange resin of either the weakly basic or the strongly basic type. The particular films described in my above-noted application are very permselective in that they allow the passage through them of anions while at the same time excluding cations. In addition they are physically strong and flexible so that they can be mounted easily in the cell. Furthermore, they are resistant to the action of chemicals and are not destroyed by the acidic solutions with which they are in contact during electrolysis. Other anionic permselective films are known such as those based on collodion; but these do not contain ion-exchange resins and are notresistant to chemicals.

What 'is required here is a film or layer containing an anion-exchange resin. Anion-exchange resins are wellknown and are widely used in the removal of ions from fluids. Suitable anion-exchange resins are described in U. S. Patents Nos. 2,106,486; 2,151,883; 2,223,930; 2,251,234; 2,259,169; 2,285,750; 2,341,907; 2,354,671; 2,354,672; 2,356,141; 2,366,008; 2,388,235; 2,402,384; 2,591,573; and 2,591,574. Some of the resins can be cast or otherwise produced in the form of free sheets or membranes. Or the anion-exchange resins can be made on a porous support such as a piece of cloth or plastic screening. As indicated above the much preferred anionic permselective membranes are those containing an anion-exchange resin, especially one of the kind described in U. S. Patents Nos. 2,591,573 and 2,591,574, dispersed as particles in a layer of a chemical-resistant matrix. Since the electric current must be carried through the permselective film by anions in association with the anion-exchange resin it is important from the standpoint of efficiency that the anion-exchange resin constitutea substantial part-at least 25% and preferably 40%- of the permselective membrane. 7 The words membrane, film, sheet, layer, and diaphragm are used synonymously herein. They de scribe the permselective barrier between the anode and cathode compartments. The barrier is usually thin, of the'order of thickness of 20 to 100 mils, although thicker membranes have been'used successfully.

The electric current is direct and a current density of about 50 to ZOO-and preferably from 90 to 180amperes per square foot is maintained. Just what current density is maintained will depend upon the construction and size of the cell and on other prevailing conditions of operation.

The salt of the amine must be Water-soluble; but the free amine itself need not be water-soluble. In fact there is an advantage when the free amine is not water-soluble because then it separates fromthe aqueous anolyte and is easily isolated therefrom. While this invention is primarily concerned with the amine salts of hydrochloric and sulfuric acids it is also true that amine salts of other inorganic acids, such as phosphoric acid, or of organic acids, such as acetic acid, can also be converted to the free amines by the process described herein.

'-The amines which can thus be liberated from their salts include primary, secondary and tertiary amines, polyamines as well as monoamines, and those containing a mixture of primary, secondary and tertiary amino groups. Typical amines which can be treated to advantage by the process of this invention include the following: methylamine, dimethylamine, trimethylamine, n-butylamine, sec.-butylamine, tert.-butylamine, -methylethlyamine, di-tert.-butylarnine, aniline, methylaniline, di-ethylaniline, pyridine, cyclohexylamine, di-cyclohexylamine, ozand ,B -naphthylamine, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, ethanolamine, dimethylamino ethanol and the like.

The particular concentration of the solution of acid Which is employed in the anode compartment at the start of the operation is not critical. It is obvious though that it should be high enough so that the current is conducted efiiciently. It should also be noted that in many instances; e. g, in the conversion of amine salts of sulfuric acid, more acid is generated in the anode compartment as the electrolysis continues. However, it is recommended that the concentration be at least one-tenth normal, andpreferably one normal, at the outset. In fact any convenient electrolyte, such as sodium chloride, can be used in the anode compartment provided its contamination of the products of electrolysis in that compartment is not objectionable.

The following example is given only to illustrate further the process of this invention.

amine salt to free amine was 85.5% complete.

4 Example An electrolysis cell of the type shown 'in'the "drawing Was employed. It was divided into an anode compartment, containing a platinum electrode, and a cathode compartment, containing a platinum electrode, by means of an anionic permselective film or membrane. The permselective film was made according to the method described in my application for Letters Patent, Serial No. 205,413, filed January 10, 1951, by dispersing on a rubber mill a commercially available anion-exchange resin (Amberlite IRA-400, sold by the Rohm & Haas Company, Philadelphia, Pa.) in a film of polyethylene. The anion-exchange resin which constituted 70% by weight of the film was 'a strongly basic quaternary ammonium resin in the hydroxyl form made by copolymerizing styrene and divinylbenzene, chloromethylating that copolymer and then reacting the chloromethylated copolymer with trimethylamine according to the process described in U. S. Patent 2,591,573.

In the cathode compartment was placed 150 parts of a 40% aqueous solution of the .hydrochloricacid salt-of ethylenediamine. In the anode compartment was placed 150 parts of a 0.1 N solution of sulfuric acid.

A direct current was passed through the cell for 30 hours 'at a current density of approximately amperes .per

square foot.

During the electrolysis, chlorine was liberatedat the anode and hydrogen was given-oil? atthe cathode. The catholyte was analyzed and was found to contain 22.7 parts of free amine. That is to say the conversionof the An'estimate of the consumption of power indicates that one pound of free 'ethylene'diamine is produced'for every 3.8 kilowatt-hours of electricity.

The process described above has been made continuous by simply flowing a solution of amine salt slowly through the cathode compartment of the electrolysis cell. The rate of flow is, of course, balanced against the current density in order to assure conversion of the aminesalt'to free amine.

I claim:

1. The electrolytic process for converting a water- 'solubleacid salt of an'amine into the corresponding free amine which comprises passing a direct current through an electrolysis cell which has a cathode compartment,

containing an aqueous solution of said water-soluble amine salt, and an anode compartment, containing an electrolyte, said compartments being separated by an anionic permselective film which contains at least 25 by weight of an anion-exchange resin.

2. The electrolytic process for converting a watersoluble amine salt of sulfuric acid into the corresponding free amine which comprises passing a direct current through an electrolysis cell which has a cathode compartment, containing an aqueous solution of said amine salt, and an anode compartment, containing an aqueous solution of sulfuric acid, said compartments being separated by an anionic permselective film which contains atlea'st 25 by weight of an anion-exchange resin.

3. The electrolytic process for converting a watersoluble amine salt of hydrochloric acid into the corresponding free amine which comprises passing afdirect current through an electrolysis cell which has a cathode compartment, containing an aqueous solution of said amine salt, and an anode compartment, containing an aqueous solution of hydrochloric acid, said compartments being separated by an anionic permselective film which "contains at least 25% by weight of an anionexchange resin.

(References on following page) 2,787,486 5 References Cited in the file of this patent OTHER REFERENCES UNITED STATES PATENTS Kalauch: Kolloid Zeitschrift, vol. 112 (1949), pp.

2363387 Bock 1944 Sollner: Journal Electrochemical Society, vol. 97, No.

2,386,926 Block Oct. 16, 1945 5 7 (July 1950), pp. 193c-150c.

2,636,851 Juda et a1 Apr. 28, 1953 I 2 3 52 Jud et 1 2 1953 pp gg s sfio He Vetlca Chlmlca Acta, VOL 23 

1. THE ELECTROLYTIC PROCESS FOR CONVERTING A WATERSOLUABLE ACID SALT OF AN AMINE INTO THE CORRESPONDING FREE AMINE WHICH COMPRISES PASSING A DIRECT CURRENT THROUGH AN ELECTROLYSIS CELL WHICH HAS A CATHODE COMPARTMENT, CONTAINING AN AQUEOUS SOLUTION OF SAID WATER-SOLUBLE AMINE SALT, AND AN ANODE COMPARTMENT, CONTAINING AN ELECTROLYTE, SAID COMPARTMENTS BEING SEPARATED BY AN ANIONIC PERMSELECTIVE FILM WHICH CONTAINS AT LEAST 25% BY WIEGHT OF AN ANION-EXCHANGE RESIN. 